A rotary stencil printing device comprises a cylindrical, ink permeable printing drum which rotates around an axial line thereof with a stencil master plate wrapped around the outer circumferential surface thereof, and a desired printing can be accomplished by pushing printing paper conveyed in synchronism with the rotation of the printing drum against the stencil master plate on the outer circumferential surface of the printing drum by using a press roller.
In such a rotary stencil printing device, printing ink is continually supplied to the printing drum from the inner circumferential surface thereof. As means for supplying printing ink in such a manner, the applicant of the present application previously proposed in Japanese patent laid open publication No. 02-37178 a squeegee device for supplying ink which pushes printing ink onto the inner circumferential surface of the printing drum by using a squeegee blade made of rubber-like elastic material which engages with the inner circumferential surface of the cylindrical printing drum and is stationary relative to the printing drum undergoing a rotary motion.
The squeegee device for supplying ink by using a squeegee blade made of rubber-like elastic material is relatively simple in structure as compared with the ink supply device of a rotary roller type using a squeegee roller, a doctor roller or the like, and has a number of advantages. However, as the rotational speed of the cylindrical printing drum increases for increased printing speed, the squeegee blade tends to develop a juddering movement or a vibration of a small amplitude, and it leads to the inconvenience that the contact pressure acting between the squeegee blade and the cylindrical printing drum is subjected to fluctuation.
Such fluctuation in the contact pressure between the squeegee blade and the cylindrical printing drum causes corresponding fluctuation in the amount of ink supply to the printing drum which in turn causes fluctuations in the density of the printed images.
Juddering of a squeegee blade diminishes as the hardness of the rubber-like material making up the squeegee blade is increased, but cannot be entirely eliminated. Further, when the hardness of the rubber-like material making up the squeegee blade is increased for reducing the tendency of the squeegee blade to judder, the intimacy of the contact between the squeegee blade and the inner circumferential surface of the printing drum tends to diminish due to the reduced tendency of the squeegee blade to undergo elastic deformation, and this leads to the unevenness of the amount of ink supply to the printing drum and the corresponding unevenness in the density of the printed images.